People like to see. The eye is a complex organ that allows a person to see his or her surroundings. The eye includes a cornea and crystalline lens that form an image on the retina of the eye. The retina of the eye senses the light image formed thereon and transmits neural signals via the optic nerve to the occipital cortex of the brain, such that the person can see and perceive his or her surroundings. Unfortunately, ocular diseases can compromise vision of the eye and may cause blindness in at least some instances.
Glaucoma is a major cause of blindness in the United States. In many instances, glaucoma related blindness can be prevented if caught and managed early. Glaucoma is usually associated with an increase in intraocular pressure (hereinafter “IOP”), that can result in damage to the retina of the eye. Because glaucoma is usually associated with an increase in IOP, periodic testing can be used to monitor glaucoma in order to prevent irreversible vision loss. For example, a person may undergo two to four exams per year in an ophthalmologist's office, although more examination may sometimes occur. Although treatment can be effective in many instances, in at least some patients may continue to lose vision under physician directed care. For example, about fifteen percent of patients under fifty years of age may continue to lose vision when receiving care and about thirty percent of patient over sixty may continue to lose vision.
A significant clinical need exists to detect elevated IOP such that appropriate medical and surgical treatment can be delivered to control the patient's IOP and decrease vision loss. Unfortunately, at least some of the current clinical techniques for measuring glaucoma may not detect elevated IOP, such that a patient can lose vision and may even become blind in at least some instances. For example, an ophthalmic exam may only measure IOP when the patient is in the eye clinic. In at least some instances, the patient may undergo an increase in IOP, for example a pressure spike, when the patient is away from the clinic. As such pressure spikes may not be detected, the patient may not receive treatment in time to mitigate vision loss. Further, at least some patients may not be able to visit the eye clinic on a strict regular basis, for example elderly patients and children, such that an increase in IOP may not be detected in a timely manner so as to prevent vision loss in at least some instances. Also, in at least some instances a patient may simply forget to take his or her medicine, such that the patient fails to follow the prescribed treatment.
Although measurements with an external IOP sensor can be helpful, these devices that measure pressure of the eye with an external sensor are somewhat indirect and can be inaccurate in at least some instances, such that the measured IOP may differ from the actual pressure inside the eye. In at least some instances, clinically available IOP sensors determine the IOP based on the externally measured pressure. For example, the IOP sensor can measure pressure of the eye on the external surface of the cornea, for example with applanation or indentation of the cornea. The externally sensed pressure of the eye can be used to determine the IOP of the eye based on assumptions about the anatomy and characteristics of the patient's eye. Such assumptions can lead to errors in the indirectly measured IOP when the anatomy of the patient deviates from the assumed normal anatomy and characteristics in at least some instances. For example, external IOP measurements can be affected by scleral rigidity influenced by topical anti-glaucoma drug therapy so as to induce errors in the externally measured IOP in at least some instances. As a result, in at least some instances a patient may not receive appropriate treatment.
Although implantable shunt devices have been proposed to treat IOP with drainage of the eye, many of these shunt devices are not well suited for patients with IOP that can be controlled without surgical intervention, for example medically controlled with drugs. In at least some instances, shunts may be used a last treatment option when other treatments such as medication and conventional surgery have failed. The insertion of such shunt devices can be more invasive than would be ideal, and in at least some instances shunt devices can cause the eye of the patient to be more susceptible to ocular trauma. For example, at least some shunt devices are designed to drain liquid from the eye and include a substantial chamber portion inserted into the sclera of the eye to drain liquid, such that the sclera of the eye may be weakened in at least some instances. Also, at least some of the current shunt devices can include rigid components that distort tissue and may result in ocular damage when the eye is subjected to trauma in at least some instances. Further, implanted shunt devices can migrate from an implanted location and can contribute to infection in at least some instances. Therefore, integration of a pressure sensor with a shunt device can result in an implant that is far more invasive and an eye that is more susceptible to injury than would be ideal in at least some instances.
It would be helpful to provide improved methods and apparatus that overcome at least some of the above shortcomings, for example with an implantable device capable of at least daily direct measurement of IOP in a manner that is less invasive than current devices, such that the improved device can be implanted in patients with medically controllable TOP. Ideally, such methods and apparatus can be implanted in the eye quickly and easily in an outpatient environment, and such that many patients can receive the benefit of direct monitoring of IOP.